Female mosquitoes require a blood meal for reproduction, and during blood feeding spread many of the devastating vector-borne diseases in humans. A deeper understanding of the molecular mechanisms linked to mosquito blood meal processes, reproductive events and anti-pathogen immunity is of particular importance for devising innovative vector control strategies. Based on strong preliminary data, we suggest that microRNAs (miRNA) play important and conserved roles in blood digestive functions of vector mosquitoes. We have developed antagomirs for depletion of miRNAs and their functional characterization in Aedes aegypti and Anopheles gambiae. We have identified two miRNAs with strong effects on blood digestion. Evaluation of spatiotemporal specificity of these miRNAs will be achieved by utilizing GAL4-UAS miRNA Tough Decoy or sponge loss-of-function transgenic mosquitoes. An important step in understanding miRNA function is determining their targets. A multi-algorithm computational target-prediction approach will be used for determination of the miRNA targets. Luciferase reporter constructs carrying 3 2UTRs of the candidate miRNA targets will then be transfected into mosquito cell lines, and their expression levels will be tested after ectopic co-transfection of a miRNA that is being studied. A phenotype rescue will be achieved by RNA interference knockdown of a target gene in the transgenic loss-of-function miRNA mosquitoes. As an alternative approach, we will identify miRNAs complementary to 32UTRs of genes encoding key enzymes involved in blood digestion and study their respective roles. This application presents a comprehensive approach for functional characterization of miRNAs in two of the most important mosquito vectors for human diseases.